The present invention is to provide a novel composite for paint curable in the air by high energy ionizing radiation (electron beams of energy as of several hundred KeV), whereby a paint film having excellent film properties can be obtained.
In recent years various studies on methods of curing paint films by high energy ionizing radiation have been carried out on a world-wide scale, and in some fields the results of the studies have been materialized even to an industrialization. In general, when considering characteristic effects to be obtained by applying the method of electron beam irradiation to a curing of paint films, there will be enumerated the following ones: (i) high speed curing, (ii) formation of paint film of high quality, (iii) no air pollution, (iv) low cost and (v) no heating operation. However, from patent specifications and articles published hitherto there could be found no resin composite, in which all of the above-mentioned items (i) to (v) could be simultaneously satisfied.
As for known resin composites curable by the irradiation of electron beams there may be mentioned, for instance, unsaturated polyester monomer type resins, epoxy monomer type resins and polyester oligomer monomer type resins and the like. Among them, the former two show considerably excellent film properties, but only in the film formability and film curability. Some of them have shown even the property of being cured in the air, which was, however, due to the existence of a volatile monomer contained in the resin composite. It is, however, to noted that in the case of using a volatile monomer as one component of the resin composite, the obtained film can not be freed from the disadvantage that the film properties will largely fluctuate on account of the volatilized amount of the monomer being different according to outside conditions. Moreover, the above-mentioned items, such as no air pollution and low cost, can not be satisfied. Further, in the case of using a polyester oligomer type monomer, it only shows a very good result in some specific properties, but is not satisfactory in the film properties, as seen synthetically.
Here some remarks will be added on the expressions "prepolymer" and "oligomer" used in this disclosure. The expression "prepolymer" designates a polymer having a molecular weight in the range of about 1000 to 10000, while the expression "oligomer" designates a polymer having a molecular weight of less than 1000.